netdev - Re: [RFC PATCH v4 net-next 1/4] tcp: replace cnt & rtt with struct in pkts

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Date:	Mon, 27 Jul 2015 19:30:39 +0000
From:	Lawrence Brakmo <brakmo@...com>
To:	Stephen Hemminger <stephen@...workplumber.org>
CC:	netdev <netdev@...r.kernel.org>, Kernel Team <Kernel-team@...com>,
	"Neal Cardwell" <ncardwell@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [RFC PATCH v4 net-next 1/4] tcp: replace cnt & rtt with struct
 in pkts_acked()



On 7/27/15, 11:46 AM, "Stephen Hemminger" <stephen@...workplumber.org>
wrote:

>On Fri, 24 Jul 2015 19:47:03 -0700
>Lawrence Brakmo <brakmo@...com> wrote:
>
>> Replace 2 arguments (cnt and rtt) in the congestion control modules'
>> pkts_acked() function with a struct. This will allow adding more
>> information without having to modify existing congestion control
>> modules (tcp_nv in particular needs bytes in flight when packet
>> was sent).
>> 
>> As proposed by Neal Cardwell in his comments to the tcp_nv patch.
>
>Adding a layer of indirection makes code changes easier, but makes
>the code slower. Arguments are passed in registers, and putting an
>additional level of indirection only matters if you can't change
>all the CC modules. Since this is the kernel and API compatability
>doesn't matter, just pass more arguments.

I prefer the cleanliness of passing a structure and don¹t think the
overhead will be significant enough to worry about it.
Will the compiler pass struct values in registers if the struct is
passed by value?

I will be happy to do it either way (I did it like Stephen proposes
originally). What does everyone else think?

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